The development and function of PMN leukocytes and megakaryocytes will be studied by high resolution electron microscopy and cytochemistry. We will investigate the following problems: a) maturation of megakaryocytes and function of platelet granules; b) changes in organelles during stimulation and suppression of thrombopoiesis; c) megakaryocyte maturation in clinical pathologic states; d) phagocytosis and degranulation in experimental and clinical studies on PMN leukocytes; e) mechanisms responsible for changes in pH of PMN phagocytic vacuole; f) role of microtubules and microfilaments in degranulation of PMN.